Various types of switching circuits are presently known in the prior art, which includes mechanical switching circuits, electronic switching circuits, and touch control switching elements. When compared to conventional mechanical switching elements, a touch control element provides a switch that has the advantages of quiet and reliable operation, spark-free operation, and extreme ease of operation by merely touching a contact or selection element. Stated differently, a switching signal is generated in response to the touch by an individual. Touch control switching elements do not incorporate any moveable mechanical parts that result in wear and, therefore, a long life is generally experienced for such elements. Touch sensitive elements are extensively used in elevators to permit an individual to select the floor level that it is desired the elevator should travel. The disadvantages to the use of a touch control switch element are that they include a higher initial cost and are difficult to apply in those applications that require a nearly continuous, rapid response, such as that provided by an electrical potentiometer, for example. The function of an electrical potentiometer has been attempted using counters, which are generally expensive and slow, or storing an electrical charge on a capacitor. The storage of an electrical charge on a capacitor is generally accompanied with the loss of charge, or a slow discharging action with time.
At the present time there is a need for a low cost form of digital logical circuitry that is useful in switching applications and can be utilized to simulate the control function of potentiometer when combined with appropriate digital to analog conversion techniques for controlling the application of power to a load, for example. The provision of such a "logical" switching circuit permits a touch sensitive control element to be utilized and which would allow a large number of control steps to be defined by the "logical" circuitry for controlling the application of electrical power to a load. When a large number of selection elements are desired to provide a large number of "logical" unique outputs, the physical space that is permitted for such a control unit may be relatively small. If such a "logical" control unit is utilized, for example, in controlling the voltage applied to a load or a lamp to function as a selection switch to control the desired light output from the lamp, the selection elements may be so close together that two or more adjacent sensors could be actuated at the same time when the touch sensitive element is actuated by an individual's finger. Accordingly, the touch sensitive element utilized in combination with "logical" circuitry should permit a preselected amount of hysteresis to be incorporated therein to overcome the problem of actuating a plurality of touch sensitive elements at the same time.
The present invention provides a "logical" data latch that is capable of detecting momentary, triggering, signals applied to its input terminals and providing a unique, latched binary output pattern or code in response to the selected latching element. The pattern of binary coded signals generated is responsive to the operation of an individual control or selection element that activates preselected logical elements in combination with the previous "logical" condition of the "logical" data latches. The "logical" data latches can be combined with touch sensitive selection control elements to effectively control the light output of a lighting device whereby the light output can be selected through the operation of sequentially arranged selection elements, or at random, to achieve the desired light output.
The basic element for the data latch of the present invention comprises a bistable latching element having at least a pair of preselected "logical" elements for defining setting and resetting portions of the bistable element. One "logical" element has a pair of input terminals coupled to be responsive to an individual binary coded triggering signal for "setting" the latching element to a preselected one of its bistable states in response to a triggering signal coupled to either one of said input terminals. The aforementioned "logical" element has an output terminal coupled thereto for signalling one of the two bistable states in accordance with the "logical" combination of the binary coded signals received at the input terminals thereof. The electronic latch includes another "logical" element having an individual pair of input terminals coupled to be responsive to individual binary coded signals for "resetting" the latching element to signal the complementary binary state from the state signalled by the setting portion of the bistable element in response to a triggering signal coupled to either one of said input terminals. The resetting "logical" element is provided with an output terminal coupled thereto for signalling the aforementioned complementary binary state in accordance with the "logical" combination of the binary coded signals received at the input terminals thereof. The bistable latching element includes first circuit means coupled between the output of the setting "logical" element to provide an input signal to the resetting logical element to assure that the output signal of the resetting logical element switches to the complementary state when the setting logical element "set" Second circuit means is provided for the bistable latching element that is coupled between the output of the resetting "logical" element and providing an additional input signal for the setting "logical" element to assure that the output signal of the setting "logical" element switches to the complementary state when the resetting "logical" element is reset. The pair of input terminals for the setting "logical" element are maintained in a preselected binary state to cause the output signal at the corresponding output terminal to signal a preselected binary state so that upon reception of a setting signal at either one of the input terminals the output terminal will be switched to signal the complementary binary state in response thereto and the output terminal of the resetting "logical" element will also be switched to the complementary binary state to assure a latched output condition. The pair of input terminals for the resetting "logical" element is maintained in a preselected binary state to cause the output signals at the corresponding output terminal to signal the complement of the preselected binary state so that upon reception of a resetting signal at either one of said input terminals, the output terminal will be switched to signal the complementary binary state in response thereto and the output terminal of the setting "logical" element will be switched to the complementary binary state to assure a latched output condition. The "logical" elements for defining the binary bistable latching element may be constructed of conventional NAND logical elements or of NOR logical elements, or combinations thereof, or any other well known form of "logical" element.
The data latch of the aforementioned type is utilized to provide a method of digitally actuating a load to vary the potential applied to the load in preselected increments including the steps of providing a preselected plurality of binary latching elements of the aforementioned type with each latching element having a pair of "setting" input terminals and a pair of "resetting" input terminals, and a pair of "set" and "reset" output terminals for the complementary signalling of the binary state of the latch. The binary latching elements are arranged in a linear sequence with the setting output terminal for each latch coupled as a setting input signal for the next lower sequential latch to cause it to be set when the next higher latch is set and with the reset output terminal for each latch coupled as a resetting input signal for the next higher latch to cause it to be reset when the next lower latch is "reset". The method includes providing individual selection elements for individually applying a selection signal to the coupled latch or latches to change the state thereof, the latch elements are caused to respond to the operation of the selection element when one of the operated selection elements sets the coupled latch to a binary 1, it will cause all latches arranged at each of the lower sequential positions to be set to a binary 1, and when the operated selection element resets a coupled latch to a binary 0, all latches arranged at each of the higher sequential positions will be reset to a binary 0 whether the selection elements are operated in sequence or at random. The binary pattern derived from the output terminals of the latches varies between all binary 0's and all binary 1's and will increase or decrease by a binary 1 in progressing from one end of the sequence of latches to the other end in accordance with the direction traversed.
This method of digital operation can be utilized to control a load such as a lamp to sequentially energize or de-energize the load or lamp in response to the pattern of binary signals appearing on the output terminals whether the data latches are operated in sequence or at random.